1. Field of the Invention
The invention relates to a method and system for separating and recovering lost circulation material from well sites during drilling.
2. Prior Art
Drilling fluid is typically used when boreholes are drilled into the earth. For example, drilling fluid is typically used when drilling oil and natural gas wells, but it may also be used for simpler boreholes, such as water wells. Liquid drilling fluid of the sort considered herein will be referred to as “drilling mud”. There are three main categories of such drilling fluids: water-based muds (dispersed and non-dispersed), and non-aqueous muds (i.e., oil-based mud, and gaseous drilling fluid), and synthetics or hybrids. Among the many benefits of using drilling fluids are that they provide hydrostatic pressure to prevent formation fluids from entering into the well bore, as well as assisting in stabilizing the wellbore. Additionally, drilling fluids cool and clean the drill bit during drilling and carry drill cuttings away from the bit to the surface. Drilling fluids additionally aid in suspending the lighter drill cuttings while drilling is paused, such as when the drilling assembly is brought in and out of the hole.
The ability of a drilling fluid to carry the rock excavated by the drill bit up to the surface depends on cutting size, shape, and density, and speed of fluid traveling up the well, i.e., it is a function of the annular velocity. The viscosity, surface tension or yield point of the drilling mud is another important consideration, since cuttings will settle to the bottom of the well if the viscosity is too low.
Lost circulation is one of the more serious problems that can arise during the drilling of an oil well or gas well. Lost circulation can be complete or partial in nature, the latter of which is usually referred to as seepage. Circulation is said to be lost when the drilling fluid, or mud, flows into the geological formations or fractures instead of returning up the annulus.
Lost circulation results in the loss of drilling fluid, which is undesirable for many reasons, including economics, wellbore stability, hole cleaning, rate of penetration, and other reasons. At times of severe seepage or lost circulation, sweeps may not sufficiently provide the relief or results desired. Additionally, loss of drilling fluids can be expensive. Hybrid water based drilling fluids, diesel based muds potassium or polymer, and even synthetic oil muds are extremely costly to lose. Lost circulation may also result in a dangerous well blowout. Therefore, well operators closely monitor tanks, pits, and flow from the well to quickly assess and control any lost circulation. If the fluid in the wellbore drops for any reason, such as lost circulation, hydrostatic pressure is reduced. The reduced hydrostatic pressure can allow a gas or fluid, which is under a higher pressure than the reduced hydrostatic pressure, to flow into the wellbore.
Another consequence of lost circulation is called “dry drilling”. Dry drilling occurs when fluid is completely lost from the well bore without actual drilling coming to a stop. Dry drilling may destroy a bit or may even require a new well to be drilled. Dry drilling can also damage the drill string, whether from increased vibration or by thermal generation and thus strength degradation.
Lost circulation material (LCM) is used to control or cease lost circulation by sealing formation pores, small holes, or fractures in the wellbore. Although fine carbonates are the most common additive used, other LCM additives are employed, depending on the fluid being used and the depth of drilling in relation to desired production zones. Other LCM additives used might include, by way of example, sawdust, flaked cellophane, crushed or ground gypsum, shredded newspaper, cotton seed hulls, cedar fiber, rubbers, etc.
To avoid loss of drilling fluids and LCM, rig vibrating separators or shale shakers are often “bypassed” completely in an effort to reclaim all or some of the LCM being directly added to the active drilling system. For short intervals this method is effective and acceptable, but over time the active pits and sand traps will become completely filled with drilled cuttings causing a loss of surface pit capacity, and an increase in drill solids within the mud system. The result can be costly time consuming pit cleanings before the next hole interval or after reaching the target depth (TD) of the well, as well as reduced rate of penetration (ROP) due to an increase in drilled and low gravity solids, increased drillstring and tool wear, reduced carrying capacity of mud, or even reduced pit volumes at the surface.
As is well known in the drilling industry, there has been a need for a system and method that would provide a better way of recovering LCM material. Accordingly, it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for a method of LCM recovery would address and solve the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.